In general, the blood plasma disappearance rate and the retention rate for testing and diagnosing of a liver function have been measured by a method of blood collection using indocyanine green (hereinafter referred to as ICG) as a specific dye.
According to the ICG method, an intravenous injection of ICG is applied to a testee and blood is collected three times after lapses of five, ten and fifteen minutes from the injection, and blood serum is separated upon coagulation of a blood clot so that absorbance at a wavelength of 805 nm is measured through a spectrophotometer to obtain ICG concentration values in the blood serum for each of the lapsed time intervals of five, ten and fifteen minutes relative to a previously obtained calibration curve (corresponding ICG concentration in blood vs absorbance), thereby to calculate the blood plasma disappearance rate and the retention rate. Japanese Patent Publication No. 60-58649 proposes a method of measuring the blood plasma disappearance rate and the retention rate without performing blood collections. According to said method, light is applied through the body surface of an organism, which in turn transmits light of a wavelength having a high ICG absorption sensitivity and light of a wavelength having substantially no ICG absorption sensitivity. The respective quantities of transmitted light are measured to obtain the blood plasma disappearance rate and the retention rate based on changes of the light quantities with time (dye disappearance curve).
Japanese Patent Laying-Open No. 64-17630 discloses an apparatus in which light is applied through the body surface of an organism and the absorbance of ICG is measured to obtain the blood plasma disappearance rate and the retention rate based on changes of the measured absorbance (dye disappearance curve). In said apparatus, a calibration is performed before measurements are made so that changes in the blood quantities in the organism, can be canceled out or disregarded.
In the conventional method of blood collection, it is necessary to correctly measure the times when blood collections are made after injection. However, under actual test conditions it is difficult to accurately measure the time and the operation for such measurement is complicated. Further, the testee is subjected to mental and physical burdens by the blood collection. In addition, the index R.sub.MAX measuring method for ascertaining the blood plasma disappearance rate repeatedly by changing the quantity of ICG injection is often used these days but said method requires several blood collections and the burdens on the testee are further increased.
According to the measuring method without blood collection as disclosed in Japanese Patent Publication No. 60-58649 mentioned above, or Japanese Patent Laying-Open No. 61-162934, the output of a sensor actually attached to an organism fluctuates in response to an influence such as blood flow disturbances caused by compression of a blood vessel, vibration of the organism subjected to the measurement, pulsation in the organism, changes in the blood volume in the vital tissue, for example, the blood volume being changed by mere vertical movement of an arm etc. Such influences make it difficult to obtain a correct dye disappearance curve.
Consequently, the blood plasma disappearance rate and the retention rate obtained by the dye disappearance curve cannot be said to be correct.
The above mentioned apparatus disclosed in Japanese Patent Laying-Open No. 64-17630 requires a calibration before any measurements can be made. Therefore, the operation is complicated. In addition, changes in the blood volume in the vital tissue can be compensated for to some extent but not in a satisfactory manner because the calibration is preferably performed immediately before an injection of a specific dye but since it takes time in reality before the injection of the specific dye becomes effective, the calibration does not effectively contribute to increasing the measurement precision.